The present invention relates to a system for delivering air to at least one suction cup, in a machine operating at high speed.
In particular, the invention relates to a delivery system intended for use in machines for working sheet materials, such as machines designed to weld the hollow cylindrical bodies of tin cans.
It is a conventional feature of automatic machines for working sheet materials, whether metallic or non-metallic, that the material is supplied to the work stations generally by means of suction cups connected to the air lines of a pneumatic system. In operation, the suction cups are connected to vacuum pumps and invested with translatory motion in relation to the sheets, which typically will be stacked one on top of another, before approaching and gripping the sheet of the stack outermost, top or bottom. The single sheet is then separated from the stack by a distancing movement of the cups and translated toward suitable conveyor means supplying the various work stations of the machine.
As the sheet must now be detached from the suction cups to allow further handling, the connection with the vacuum pumps will be cut off at the appropriate moment, and the cups thus vented to the atmosphere. The connections in question are controlled in most instances by means of pneumatically actuated three way valves, forming part of the delivery system, which can be purchased in a wide variety of types and versions.
It has been observed that the use of these valves in machines operating at particularly high speeds, that is, with sheets supplied at a rate of several hundreds per minute, tends to be accompanied by a variety of drawbacks (attributable to shortcomings in the pneumatic control system), which are both of key importance in practical terms and pivotal as regards their combined influence on the functional effectiveness of the machine.
In practice, the time taken to neutralize negative pressure through the suction cups on the completion of each operating cycle tends to be unduly long: a drawback stemming from the length of the pipelines connecting the cups to the valves, which disallows a rapid flow of air through the bore; accordingly, the slow response of the cups on release has to be compensated by using pumps of large capacity which produce only a partial remedy, and at a high cost. It is also very difficult in general to synchronize the action of the suction cups with the work cycles of other sections of an automatic machine running at high production tempo, given that the operating rhythm will be affected even by the slightest of inertia forces, however generated.
With the slowness in response of the suction cups mentioned above, the difficulty in synchronizing pick-up and release of the sheet with the operation of the remainder of the machine is much increased, and especially at the moment of release, by reason of the consistent quantity of air that has to be controlled; in effect, the suction cup (together with the corresponding pipeline) functions as a restraint (mechanically as well as pneumatically), even after deactivation of the aspirating effect, for a duration that is by no means negligible.
Taken overall, the drawbacks mentioned above are instrumental in essentially disallowing a genuinely high speed and at the same time precise operation of automatic machines for working sheet materials; in terms of numbers, this signifies that operating speeds of the order of 800-850 strokes per minute are unobtainable, albeit well within the scope of such machines if the right infeed is provided.
Accordingly, the object of the present invention is to provide an air delivery system, connected to at least one suction cup, such as will overcome the drawbacks mentioned above while ensuring precision and dependability in operation of the high speed machines with which the disclosure is concerned. In this context, it is also an important object of the invention to provide a delivery system of the type in question that is simple in construction, inexpensive and easily carried into effect by any operator in the relative industrial sector.